1. Field of the Invention
The present invention relates to a secondary battery and an electronic instrument using it, and more specifically to a secondary battery composed of battery element and an external packaging film sealing the battery element by adhering thereto and also to an electronic instrument using it.
2. Description of the Related Art
By the propagation of lithium ion batteries or the like, small-sizing and light-weighting of a battery as the electric source of portable type electronic instruments such as a portable telephone, etc., have rapidly progressed. However, the requirement of more small-sizing and thinning of electronic instruments is strong, and more small-sizing and thinning of batteries have been demanded. In such a circumstance, small-sizing and thinning of various electronic parts have been attempted, at present, the size of a battery becomes an essential factor of determining the size or the thinness of electronic instruments, and many efforts have been made for thinning and light-weighting of batteries.
For thinning electronic instruments, it is preferred to mount a battery having as small a thickness as possible. For determining the position of the battery in the instrument needs to be considered according to an inside configuration of the instrument. That is, in a thin battery, a sufficient capacity is not obtained, whereby the using time is restrained, and when a thick battery is used for obtaining a sufficient capacity, thinning of electronic instrument becomes difficult.
Thus, in the stage of circuit designing, an effort of insuring a wide space having a uniform thickness by gathering parts having a high height at one portion has been made but in such a case, it is unavoidable that the degree of freedom of circuit designing is spoiled.
In such circumstances, thinning of a secondary battery of portable type electronic instruments has progressed, and recently, can-type secondary batteries having a thickness of 4 mm or thinner have been commercialized and card-type or film-form batteries utilizing laminate pack have been developed, but the above-described problems have not yet been fundamentally solved.
The present invention has been made in view of the above-described problems, and an object of the invention is to provide a secondary battery having a sufficient capacity and capable of attaining small-sizing and thinning of electronic instruments without spoiling the degree of freedom of circuit designing and to provide an electronic instrument using the secondary battery.
According to the present invention, there is provided a secondary battery comprising a battery main body composed of at least one battery element and an external packaging film, the battery element including an electrolyte as well as a positive electrode layer and a negative electrode layer holding the electrolyte therebetween, the external packaging film closely contacting and sealing the battery element, wherein the external packaging film sealing the battery element has, at a surface thereof, a difference in level according to a contour of the battery element.
That is, in the case of forming the battery main body of the secondary battery by laminating battery elements each, as the fundamental unit, composed of a positive electrode, an electrolyte, and a negative electrode, by partially changing the laminated layer number of the battery elements, the difference in level fitting to the form of the receiving space of the secondary battery or the form of electronic part group received adjacent to the secondary battery can be formed at the surface of the battery main body, whereby the secondary battery capable of being deformed without being adhered to the restriction of the uniform thickness of a secondary battery of prior art can be provided.
That is, in the secondary battery of the invention, since in the designing stage of an electronic instrument constituted together with an electronic part group, an external packaging case, etc., each of high and low portions can be desirably established at the battery main body. For example, in the case of placing a secondary battery adjacent to an electronic part group received in an external packaging case, a secondary battery having high and low portions absorbing the unevenness of the height of the electronic part group can be prepared or a secondary battery having high and low portions fitting to the space having nonuniform shapes in the above-described external packaging case can be prepared.
Also, according to other view point of the present invention, there is provided a secondary battery wherein constituting members such as circuit portions, etc., constituting an electronic instrument are disposed on the surface of the battery element and they are sealed with an external packaging film, whereby the difference in level is formed between a high portion composed of the surface of the constituting members such as the above-described circuit portions, etc., disposed on the surface of the battery element and a low portion composed of the exposed surface of the battery element, and such a secondary battery is also included in the invention.
As the circuit portions in the invention, protective circuit portions of an electronic instrument are illustrated. In this case, the battery main body may be a battery main body of prior art having a uniform thickness only or the battery main body may be the battery main body having the portions having large and small laminated numbers of the battery elements of the invention.
By the construction as described above, the secondary battery having a sufficient capacity can be mounted on an electronic instrument while utilizing in maximum the restricted receiving space.
Since when an adhesive packaging technique which has hitherto been used for sealing a battery element with an external packaging film by adhesion is applied to the present invention, the difference in level according to the above-described high and low portions is formed as it is on the surface of the external packaging film of the battery element, the technique can be applied without obstructing the establishment of the correct difference in level.
Accordingly, the secondary battery having a sufficient capacity and capable of attaining small-sizing and thinning of an electronic instrument can be proposed without spoiling the degree of freedom of circuit designing.
The difference in level is formed by a plurality of planes perpendicular to a direction in which the electrolyte and the positive and negative electrode layers of the battery element are laminated.
xe2x80x9cThe high portionxe2x80x9d in the secondary battery of the invention means xe2x80x9cthe surface of a thick portionxe2x80x9d of the battery element where a relatively large number of layers are laminated, and xe2x80x9cthe low portionxe2x80x9d means xe2x80x9cthe surface of a thin portionxe2x80x9d of the battery element where a relatively small number of layers are laminated.
As the embodiments of the lamination of the battery elements for forming the difference in level at the external packaging surface of the secondary battery of the invention, there are illustrated embodiments such as (1) a small battery element is placed on a large battery element, (2) one battery element is wound, (3) one battery element is folded a little, etc.
As the above-described embodiment (1), there is illustrated an embodiment that the difference in level is formed between a high portion defined by a surface of a second battery element which is laminated on a surface of a first battery element and is smaller than the first battery element and a low portion defined by an exposed surface of the first battery element.
As the above-described embodiment (2), there is illustrated an embodiment that the battery element is wound round, and the difference in level is formed between a high portion defined by a surface of an outside end portion of the battery element and a low portion defined by an exposed surface of the battery element below the outside end portion.
As the above-described embodiment (3), there is illustrated an embodiment that the battery element is folded, and the difference in level is formed between a high portion defined by a surface of an upper end portion of the battery element and a low portion defined by an exposed surface of the battery element below the upper end portion.
In the present invention, the phrase xe2x80x9ca low portion defined by an exposed surface of a battery elementxe2x80x9d means that a low portion is defined by a surface of the battery element or battery main body and that, inside the packaging, the surface is not covered with another battery element, a part of the battery element or battery body itself, or another element of the secondary battery such as a circuit portion.
In the embodiments (1) to (3) described above, there are no particular restrictions on the lamination layer number of the battery elements, the formation number of the high and low portions, the formation positions of the high and low portions, the formation directions (same directions/opposite directions) of the high and low portions, the winding number of the battery element, the folding number or the combination of the folding directions (outer folding/inner folding) of the battery element.
In addition, in the embodiments (2) and (3), by establishing the length of the end portion of the battery element such that the end portion is disposed at the desired position of the electrode surface of the battery element becoming the low portion, the width of the high portion is determined.
xe2x80x9cThe high portionxe2x80x9d in the secondary battery in other view point of the invention means xe2x80x9cthe surface of a thick portionxe2x80x9d of the battery main body containing the circuit portion disposed on the surface of the battery element, and xe2x80x9cthe low portionxe2x80x9d of the battery main body means xe2x80x9cthe surface of a thin portionxe2x80x9d composed of the battery element only without containing the circuit portion.
As the practical embodiment of forming the difference in level on the external packaging surface of the secondary battery of the invention, there is illustrated an embodiment that a protective circuit (circuit portion) of an electronic instrument is disposed on the surface of the battery element.
In the embodiment of the secondary battery containing the above-described circuit portions, there are no particular restrictions on the disposed number, the disposed positions, and the disposed directions (same directions/opposite directions) of the circuit portions.
In addition, the secondary batteries each disposing the above-described circuit portions on the surface of the battery element of the embodiments (1) to (3) described above are also included in the invention.
By adhering the external packaging film in the invention to the battery element by vacuum packaging, the difference in level of the battery element forms the difference in level of the surface of the battery main body as it is. In vacuum packaging, in the case of sealing the battery element with the external packaging film, when the inside is evacuated and the battery element is sealed as it is, the external packaging film is pressed by the atmospheric pressure, by the flexibility of the external packaging film, the external packaging film becomes a concave form towards outside in the corner portion, etc., between the high portion and the low portion of the battery element, and the difference in level is definitely formed at the surface of the battery element while minimizing the gap between the inside surface of the external packaging film and the battery element.
The difference in level of the surface of the battery main body in the invention is the range of from 10 xcexcm to 2 mm, and preferably from 100 xcexcm to 1 mm. When a battery main body is not mounted on an instrument by the slight difference of thickness in the designing stage of the instrument, such a level difference of the battery avoid a large designing change of circuit and the space of the instrument is efficiently utilized. When the above described level difference is too large, the energy density of the battery element inserted in the thin portion is lowered, and, on the other hand, when the level difference is too small, the fundamental unit of the battery element cannot be received.
The area ratio of the surfaces of the high portion and the low portion can be properly selected but it is desirable that the area ratio of the area of the thin portion/the area of the thick portion is from 0.5/9.5 to 9.5/0.5, preferably from 0.5/9.5 to 5/5, and more preferably from 0.5/9.5 to 3/7.
Also, it is preferred to insure the battery capacity that the area of the surface of the low portion is kept at a minimum. The form of the boundary forming the difference in level is preferably a straight form which can be easily formed but the form may be a bent line form or a curved line form, and the form can be selected to be the form which is most useful in the case of mounting the battery on an instrument.
As the electrolyte in the invention, it is preferred to use a solid polymer electrolyte. By using a solid polymer electrolyte as the electrolyte in the invention, the safety is increased and even when the external packaging film is a thin external packaging material such as a laminate material, the battery having a high reliability can be obtained.
According to another view point of the present invention, there is provided an electronic instrument comprising the secondary battery of the invention described above, an electronic part group, and an external packaging case, wherein by disposing the high portion and the low portion forming the difference in level of the surface of the external packaging film of the secondary battery to the electronic parts having different heights or the wall surfaces of different heights in the inside of the external packaging case, the secondary battery and the electronic part group are placed in the external packaging case in a dense state.
The electronic instrument in the invention means an electronic instrument constituting one independent electronic apparatus or electric apparatus by combining the secondary battery of the invention described above with an electronic part group, etc., and an electronic instrument constituting a circuit assembly forming at least a part of the circuit portions of an electronic apparatus or an electric apparatus by combining the secondary battery of the invention with an electronic part group, etc.
Since in the electronic instrument of the invention, the degree of freedom for circuit designing is increased and the secondary battery having a sufficient capacity can be mounted by effectively using the space of the electronic instrument, as compared with an electronic instrument of prior art, the thin-type electronic instrument can be prepared without shortening the using time of the electric source. The electronic instrument of the invention include a potable terminal, that is, potable information instrument such as a portable telephone, a notebook personal computer, electronic pocketbook, etc.; a potable-type game device, a card-type computer, a digital camera, etc.